BACKGROUND: Eosinophils rapidly undergo apoptosis unless exposed to prosurvival cytokines such as interleukin 5 (IL-5) or granulocyte-macrophage colony stimulating factor (GM-CSF). In vivo, eosinophils are exposed to TGF-β 1 which can induce apoptosis suggesting it may function to counteract the effects of IL-5 or GM-CSF and limit, in vivo tissue eosinophilia. OBJECTIVE: The objective of this study was to investigate the proapoptotic effects of TGF-β alone and in combination with IL-5 on eosinophils. METHODS: Peripheral blood eosinophil (PBEos) viability was assessed using flow cytometry after exposure to TGF-β1 and IL-5. Calpain-1 activation was determined in cell extracts by western blot analysis of endogenous substrates and with a fluorogenic α-spectrin substrate. Molecular interactions between calpain1 and calpastatin were assessed by immunoprecipitation and western blotting. RESULTS: Physiologic concentrations of TGF-β1 significantly antagonized the prosurvival effects of IL-5. TGF-β1-induced apoptosis was suppressed by inhibitors of calpain, or its downstream target, caspase 3. TGF-β1 signaling through Smad3 was unaffected by IL-5 and was required for the pro-apoptotic effects of TGF-β1. However, IL-5 induced Akt phosphorylation was inhibited by TGF-β1 and was associated with accelerated calpain cleavage and eosinophil death. CONCLUSION: TGF-β1 induces calpain-1 activation through antagonism of Akt which induces caspase activation and eosinophil apoptosis.
BACKGROUND: Eosinophils rapidly undergo apoptosis unless exposed to prosurvival cytokines such as interleukin 5 (IL-5) or granulocyte-macrophage colony stimulating factor (GM-CSF). In vivo, eosinophils are exposed to TGF-β 1 which can induce apoptosis suggesting it may function to counteract the effects of IL-5 or GM-CSF and limit, in vivo tissue eosinophilia. OBJECTIVE: The objective of this study was to investigate the proapoptotic effects of TGF-β alone and in combination with IL-5 on eosinophils. METHODS: Peripheral blood eosinophil (PBEos) viability was assessed using flow cytometry after exposure to TGF-β1 and IL-5. Calpain-1 activation was determined in cell extracts by western blot analysis of endogenous substrates and with a fluorogenic α-spectrin substrate. Molecular interactions between calpain1 and calpastatin were assessed by immunoprecipitation and western blotting. RESULTS: Physiologic concentrations of TGF-β1 significantly antagonized the prosurvival effects of IL-5. TGF-β1-induced apoptosis was suppressed by inhibitors of calpain, or its downstream target, caspase 3. TGF-β1 signaling through Smad3 was unaffected by IL-5 and was required for the pro-apoptotic effects of TGF-β1. However, IL-5 induced Akt phosphorylation was inhibited by TGF-β1 and was associated with accelerated calpain cleavage and eosinophil death. CONCLUSION: TGF-β1 induces calpain-1 activation through antagonism of Akt which induces caspase activation and eosinophil apoptosis.
Authors: Erica M Pasini; Morten Kirkegaard; Peter Mortensen; Hans U Lutz; Alan W Thomas; Matthias Mann Journal: Blood Date: 2006-08-01 Impact factor: 22.113
Authors: Wei Duan; Ana M K Aguinaldo Datiles; Bernard P Leung; Chris J Vlahos; W S Fred Wong Journal: Int Immunopharmacol Date: 2005-03 Impact factor: 4.932
Authors: Ming O Li; Yisong Y Wan; Shomyseh Sanjabi; Anna-Karin L Robertson; Richard A Flavell Journal: Annu Rev Immunol Date: 2006 Impact factor: 28.527